Stroke
A stroke, or cerebrovascular accident as otherwise known, is defined as a rapidly developing loss of brain function due to a disturbance in the blood supply to the brain. This can be due to ischemia (lack of blood supply) caused by thrombosis or embolism or due to a hemorrhage. As a result, the affected area of the brain is unable to function, leading to the inability to move one or more limbs on one side of the body, the inability to understand or formulate speech, or the inability to see one side of the visual field amongst others.
Each year, about 800,000 people experience a new or recurrent stroke. Approximately 600,000 of these are first attacks, and 200,000 are recurrent attacks. In addition, and on average, someone in the U.S. has a stroke every 40 seconds, and each year about 55,000 more women than men have a stroke. On average, every 3-4 minutes, someone dies of a stroke. Because women live longer than men, more women than men die of stroke each year. Women accounted for 60.6% of U.S. stroke deaths in 2005. Men stroke incidence rates are greater than women at younger ages but not at older ages. Despite advances in stroke prevention treatments, the incidence of hospitalized stroke and case fatality did not decrease. African-Americans have almost twice the risk of first-ever stroke than whites. The age adjusted stroke incidence rates in people 45-84 years of age are 6.6 per 1000 population in black men, 3.6 in white men, 4.9 in black women, and 2.3 in white women.
Of all strokes, 87% are ischemic, 10% are intracerebral hemorrhage, and 3% are subarachnoid hemorrhage strokes. Stroke accounted for about 1 out of every 17 deaths in the U.S. in 2005, and approximately 53% of stroke deaths in 2005 occurred out of the hospital.
Total stroke mortality in 2005 was about 150,000. The 2005 overall death rate for stroke was 46.6 per 100,000. Death rates were 44.7 for white males, 70.5 for black males, 44.0 for white females, and 60.7 for black females, all per 100,000. When considered separately from other cardiovascular diseases, stroke ranks no. 3 among all causes of death, behind heart disease and cancer. Moreover, stroke is the leading cause of serious, long-term disability in the United States. Indeed, it is widely recognized that strokes are a major cause of adult disability due to both the debilitating initial symptoms and in many cases severe long-term impairment.
A report released by the Centers for Disease Control (CDC) in collaboration with the Centers for Medicare and Medicaid Services (CMS), the Atlas of Stroke Hospitalizations Among Medicare Beneficiaries, found that in Medicare beneficiaries, 30-day mortality rate varied by age: 9% in patients 65 to 74 years of age, 13.1% in those 74 to 84 years of age, and 23% in those 85 years of age. Accordingly, it is clear that prevalence of stroke is associated with substantial health, quality of life and economic costs.
Atrial Fibrillation
Atrial fibrillation (AF) is a significant, independent risk factor for ischemic stroke, increasing risk about 5-fold. The percentage of strokes attributable to AF increases steeply from 1.5% at 50 to 59 years of age to 23.5% at 80 to 89 years of age. Most strokes in patients with AF are cardioembolic caused by embolism of left atrial appendage thrombi, but some are caused by coexisting intrinsic cerebrovascular diseases in typically elderly, often hypertensive patients.
AF carries an annual risk of thromboembolic complications of 3-6%, which is 5-7 times greater than that of controls with sinus rhythm. AF is present in 15-21% of patients affected by stroke. AF/flutter, a strong risk factor for stroke, is arguably the most important finding on cardiac workup in patients with ischemic stroke. Once identified, introduction of oral anticoagulant therapy (warfarin, for example) provides a 40% risk reduction in recurrent stroke compared with antiplatelet therapy. Ischemic stroke with AF is associated with greater disability and mortality than those without AF. However, not all patients can receive anticoagulant or antiplatelet therapies, and the same or other patients may be prone to clots that form in the left atrial appendage and enter the bloodstream, so other types of therapies would be required.
Patients with AF have an increased risk of major, disabling stroke, often caused by large infarctions in the middle cerebral artery territory. Some studies showed that AF was associated with an increased risk of death in the first four weeks after stroke likely due to the advanced age in stroke patients with AF, large infarction, severe neurological deficits, and poor functional outcomes.
First, strokes in patients with AF may largely be cardioembolic, which causes a sudden occlusion of large cerebral arteries without sufficient collateral blood flow, resulting in more severe strokes. Several studies have reported that stroke patients with AF often have large cortical infarcts on computed tomography, and less frequently have lacunar infarction as compared with patients without AF.
Heart Failure
Patients with heart failure (HF) are at increased risk for thromboembolic events. Left ventricular (LV) thrombus provides a substrate for events and a rationale for anticoagulation. Echocardiography studies have yielded conflicting results, however, regarding thrombus prevalence. Among populations with similar degrees of systolic dysfunction, studies have reported over a 20-fold difference in prevalence, ranging from 2.1% to 50%. Moreover, when thrombus is identified, conflicting findings have been reported concerning the risk of future embolic events.
The impact of nonrheumatic atrial fibrillation, hypertension, coronary heart disease, and cardiac failure on stroke incidence was examined in the Framingham Study. Compared with subjects free of these conditions, the age-adjusted incidence of stroke was more than doubled in the presence of coronary heart disease and more than tripled in the presence of hypertension. There was a more than fourfold excess of stroke in subjects with HF and nearly fivefold increase when atrial fibrillation was present. In persons with coronary heart disease or HF, atrial fibrillation doubled the stroke risk in men and tripled the risk in women. Factors that predispose to thromboembolic events in patients with HF include low cardiac output, with relative stasis of blood in dilated cardiac chambers, poor contractility and regional wall motion abnormalities and concomitant atrial fibrillation.